Battery and method of making the same

ABSTRACT

Applying materials, e.g. electrolytes and other materials, in the form of a spray during battery manufacture, particularly using a vibratory nebulizer to produce a small droplet, low velocity spray.

TECHNICAL FIELD

This invention relates to battery manufacture.

BACKGROUND

Most batteries are constructed using a container, known as a can, thatholds reactive chemicals that drive the battery by electrochemicalreactions. The chemicals are usually divided by a separator. Anelectrolyte fluid facilitates ionic flow between the chemicals andacross the separator to develop an electric potential.

Generally, alkaline batteries include a cathode, an anode, a separator,and an electrolytic solution. The cathode is typically formed of anactive material (e.g., manganese dioxide), carbon particles, and abinder. The anode can be a gel including an active material (e.g., zincparticles). The separator is usually disposed between the cathode andthe anode. The electrolytic solution, which is dispersed throughout thebattery, can be a hydroxide solution. Alkaline batteries include theconventional AA, AAA, AAAA, C, and D batteries commonly sold in stores.These conventional alkaline batteries include a cylindrical containercontaining a central, cylindrical zinc gel anode surrounded by a thinseparator, which is in turn surrounded by a ring-shaped cathode.

In the manufacture of alkaline batteries it is common to start with acylindrical can to which is first added a pelletized cathode materialthat is in the shape of an annulus. A separator is then placed againstthe surface of the cathode inside the annulus. The separator may be apreformed cylindrical sheet of, e.g., cellulose material, or theseparator may be material that is applied as a liquid and then forms astable film. A small precharge of electrolyte is then added to wet theseparator. The precharge is poured into the annular opening defined bythe separator and forms a small pool at the bottom of the can from whichit wicks into the separator after a period of time. After the pool hasbeen substantially depleted by the wicking action, the anode material,typically a slurry containing, for example, zinc particles, is added tothe opening. Allowing time for sufficient wicking is important so thataddition of the anode slurry does not displace the pool and causespillage of electrolyte over the top of the can.

SUMMARY

In an aspect, the invention features a method for applying material inthe manufacture of a battery including applying the material in the formof a spray generated from an vibratory nebulizer.

In another aspect, the invention features a method for applyingelectrolyte in the manufacture of a battery, including applying theelectrolyte in the form of a spray.

In another aspect, the invention features a method for applying aseparator in the manufacture of a battery, including applying afilm-forming system that forms a film. The system includes a firstcomponent and a second component. The first and second component areapplied simultaneously as a spray.

In another aspect, the invention features a method for applying materialin the manufacture of a battery. The method includes selecting amaterial to be applied and applying the material in the form of a sprayhaving an average droplet size of about 1 micron to about 75 micronless.

Embodiments may also include one or more of the following. The dropletsize is about 5 micron to about 30 micron. The spray velocity is about10 inch/sec or less, preferably about 3 to about 5 inch/sec. The methodincludes providing a separator and applying the electrolyte to at leastone portion of the separator. The method includes providing theseparator in a battery can prior to the applying the material byspraying. The method includes applying the electrolyte such thatsubstantial pooling of the electrolyte in the bottom of the can isavoided. The spray is formed by an ultrasonic nebulizer. The material isa film-forming material suitable as a separator. The method includesproviding a cathode and applying the film-forming material to at least aportion of the cathode. The method includes providing the cathode in acan prior to applying the film-forming material. The method includesfacilitating film-forming by application of a second component, thesecond component being applied as a spray. The second component isapplied sequentially with the film-forming material. For example, thesecond component may be supplied after application of the firstcomponent or the second component may be applied prior to the firstcomponent. The second component is applied simultaneously with thefilm-forming material. The film-forming material is PVA. The PVA is filmformed by application of electrolyte. The PVA and electrolyte areapplied sequentially. The PVA and electrolyte are appliedsimultaneously. The battery has a non-cylindrical electrode surface,such as a lobed surface, and the material, e.g. separator material, isapplied as a spray originating near the axis of the battery. The batteryis an alkaline battery.

Embodiments may provide one or more of the following advantages.Application of materials during battery manufacture by providing thematerials in the form of a low velocity, small droplet spray canincrease the uniformity of the application, reduce the time required forapplication, eliminate processing steps, and provide separators andother components with new and advantageous characteristics. For example,spray application of a precharge of electrolyte to a separator providesa highly uniform application of the electrolyte and also eliminates theneed to await wicking of electrolyte from a pool of electrolyte that isformed by initially pouring a pre-shot of the electrolyte into thecavity prior to introduction of the anode slurry. Application offilm-forming separator material in the form of a spray provides a highlyuniform separator that is easily integrated into a manufacturingenvironment. A vibratory nebulizer, particularly ultrasonic nebulizers,provide substantial advantage in application of materials during batterymanufacture. The drop size and velocity-tunable, generally low momentummist or aerosol generated by such nebulizers allows a low velocityapplication without generating substantial turbulence or splattering inthe tight confines of the battery can environment. Moreover, velocityand drop size can be adjusted. The nebulizer tip diameters arerelatively small, making them applicable to the narrow diameter of avariety of battery can sizes.

Still further aspects, features, and advantages follow.

DESCRIPTION OF THE PREFERRED EMBODIMENT

We first briefly describe the drawings.

Drawings

FIG. 1 is a schematic of a system for low velocity, small droplet sprayapplication of materials in battery manufacture;

FIG. 2 is a cross-section of an ultrasonic nebulizer;

FIGS. 3, 3A, 3B, 3C, 3D and 3E are cross-sectional side viewsillustrating battery manufacture using application of materials as aspray;

FIGS. 4, 4A, 4B, 4C, 4D, 4E and 4F are cross-sectional side viewsillustrating another embodiment of battery manufacture; and

FIGS. 5, 5A and 5B are end-on views illustrating another embodiment ofbattery manufacture.

DESCRIPTION

Nebulizer System

Referring to FIG. 1, a system 2 for application of material as a sprayof low velocity, small droplets during battery manufacture includes anebulizer 4 , including a probe 22, which is assembled by a clamp 9 andon a positioner 6 that permits vertical displacement (arrows 7, 15) ofthe nebulizer over an assembly line conveyor 8 including batterycomponents such as a battery can 10. The nebulizer is connected to afluid supply 12 and a power source 14. The vertical positioner has acontroller 16. A monitor 20 is provided for monitoring the position ofthe battery components on the assembly line and/or monitoring the statusof the material application from the nebulizer. The overall operation isdictated by a system controller 16. In operation, a desired material,e.g., electrolyte, is provided from the supply 12 to the nebulizer. As abattery can comes to the application station, the nebulizer is loweredsuch that the nebulizer probe 22 is disposed in the can and nebulizationis initiated to form a compact spray 11 for applying an aliquot 13 ofmaterial to the internal battery surfaces. The nebulizer can betranslated upward (arrow 15) or alternatively, downward, duringnebulization, to apply the material to the full extent of the internalsurfaces within the can.

Referring as well to FIG. 2, the nebulizer may be a vibratory nebulizer,such as an ultrasonic nebulizer. The ultrasonic nebulizer includes ahousing 24 and a probe 22. The housing includes piezoelectric elements26 which are powered by alternating signal via line 28 to imposevibrating motion on the proximal portion of the probe 22. The frequencyof the signal is chosen in coordination with the design (particularlylength) of the probe to produce vibrating action at the tip 30 of theprobe. The probe also includes a liquid feed path 32 along its length.Material to be sprayed is delivered from the supply to the near end ofthe feed path 32 and expelled from the opening 34 at the tip 30. Thevibratory motion of the tip breaks the emerging fluid into a spray.

The velocity and size of the spray in the spray can be controlled bycontrolling the power and frequency supplied to the nebulizer and theshape of the probe. The droplets are sized small enough so that theyuniformly and efficiently coat the surface, such as the surface of aseparator which can, for example, yield faster wicking when wetting aseparator with electrolyte, but droplets which are too small may becarried by microcurrents away from the surface to which they are beingapplied. The droplet size can be reduced by increasing the ultrasonicfrequency. Preferably, the average droplet size is in the range of about1 to about 75 micron, more preferably about 5 to about 30 micron, mostpreferably about 10 to about 25 micron. Droplet size can be measured bylaser interferometry.

The velocity of the spray is selected to produce a fine, low energy mistthat applies the droplets smoothly without causing them to excessivelybounce off the application surface or create turbulence in the confinesof the can that can lead to mist formation outside the application area(overspray). The velocity must be high enough to permit the droplets toreach the application surface before gravity or other interactionssignificantly alter their course. The velocity of the droplets can becontrolled by the controlling the power level supplied to the nebulizer.Preferably, the spray velocity is about 10 inch/sec or less, morepreferably about 3 to about 5 inches/sec. Spray velocity can be measuredby laser interferometry.

The nebulizer probe is typically sized to fit inside the opening withinwhich the material is to be supplied and has a length that permitsapplication into the deepest reaches of the can. The probe diameter issmall enough so that the spray forms a stable, low velocity mist, suchthat a substantial portion of the initial energy imparted to thedroplets has been dissipated by the time they reach the applicationsurface. An advantage of the ultrasonic nebulizer is that the spray isprojected forward away from the tip of the probe which permits evenapplication to the deepest portions of a can, including the interfacebetween the bottom of the can and the separator. The probe diameter ispreferably about 25% or less than the diameter of the opening. The probecan be sized for delivery into openings having diameters between about 2mm to about 20 mm and depths to about 2 inch common to standard sizebatteries. For AA size batteries, for example, which have been partiallyassembled by including cathode pellets and a separator, the centralopening has a diameter of about 0.35 inch and a depth of about 1.7 inch.For AAA size batteries, for example, which have been partially assembledby including the cathode pellets and a separator, the central openingtypically has a diameter of about 0.23 inch and a depth of about 1.6inch. Suitable nebulizers, probes, and power supplies are available fromMisonix (e.g. Model Micromist 640 system/P80 probe, Misonix,Farmingdale, N.Y.). The Misonix nebulizer has a maximum output power ofabout 35 watts and operates at a frequency of about 40 KHz. The probesize is {fraction (5/16)} inch×2¼ inch with a tip diameter of 0.110inch. The tip has a truncated cone shape and an amplitude of about 70microns. The droplet size is about 20 microns average and the spraypattern is generally torroidal. The flow rate capacity is about 0.1 toabout 30 cc/min. Suitable nebulizers are also available from Sono-Tek(e.g., Model BD type, Sono-Tek, Milton, N.Y.).

Further discussion regarding ultrasound nebulization andcharacterization of ultrasound sprays is provided in “Ultrasound LiquidAtomization, Theory and Application” by Harvey L. Berger, Partridge Hillpublishers (available from Sono-Tek, Milton, N.Y.), the entire contentsof which is incorporated by reference.

The fluid supply 12 may be a peristaltic or syringe pump, gear pump,pressurized reservoir or gravity feed. A syringe pump or pressurizedreservoir is preferred since these techniques minimize pressurevariations during application. For film-forming materials, the plumbingbetween the supply and nebulizer can be heated with heating tape.Preferred fluid supply systems have a delivery accuracy of about 1ml±0.2 ml. Suitable systems are available from Ivec, North Springfield,Vt. and HiBar, Toronto, Canada.

The positioner 6 and positioner controller 16 can be a motorizedvertical controller or an X-Y digital positioner. The nebulizerpositioner and positioning apparatus for the can preferably have anaccuracy of about 0.0005 inch. The overall control can be achieved bysoftware and/or hardware. Coating and assembly line monitoring can beachieved by spectroscopic techniques.

Separator Wetting

Referring now to FIGS. 3-3E, spray application of a pre-charge ofelectrolyte for wetting a pre-formed separator is illustrated. Referringparticularly to FIGS. 3 and 3A, the can 10 is first provided with aseries of annularly shaped cathode pellets 40. Referring to FIG. 3B, apre-formed cylindrical separator 42 is then inserted into the centeropening of the cathode pellets. The separator may be, e.g., a sheet ofcellulose material shaped into a cylinder. Referring to FIGS. 3C and 3D,a pre-load of electrolyte is then applied as a spray 41 to wet theseparator without forming a substantial pool of electrolyte in thebottom of the can. The preload is applied as a spray by positioning thenebulizer probe 22 in the can and beginning nebulization. The probe isdrawn upward (arrow 43) during nebulization. The low velocity, evendistribution of electrolyte in the form of small drops quickly wets theseparator. In batteries with a positive pip on the bottom of the can,collection of a small pool of electrolyte in the pip dead volume ispermissible. As a result, no substantial waiting period is needed beforeadding the anode slurry. Referring to FIG. 3E, after the probe isremoved from the can, the anode slurry 44, including the remainingelectrolyte, is immediately dispensed into the can. The battery can thenpass to other steps of manufacture such as assembling and crimping thetop assembly.

In the application of electrolyte such as 9N KOH solution, the averagedroplet size is about 10 to about 20 micron, and the power is about 8-12watts. The probe is lowered to about 0.1 inch from the bottom of the canand drawn vertically at a rate of about 0.5-1.5 inch/sec. The flow rateis about 0.3-1.0 ml/sec. Typically about 20-50% (by weight) of the totalelectrolyte content of the battery may be applied in the wetting step.In alternative embodiments, the separator may be wetted prior toinsertion in the can. Application of electrolyte to the anode or cathodematerial either prior to or after delivery to the can may also becarried out by spraying.

In further embodiments, the cathode may be wet with electrolyte prior toproviding the separator. For example, a can with the cathode pellets maybe provided as shown in FIG. 3A. An electrolyte is then applied to thecathode, followed by insertion of a preformed separator or applicationof a film-forming separator, followed by wetting the separator, followedby delivery of the anode material. For example, the cathode may be wetby spray application with about 5-15% by weight, preferably about 10% ofthe total electrolyte, followed by insertion of a preformed separatorwhich is wet by spray application with about 15-40%, preferably about20% of the total electrolyte. As a result, substantially 40% or more ofthe total electrolyte may be applied in the wetting steps by sprayapplication. The total electrolyte for a AA battery, for example, may beabout 3.1 g.

Separator Application

Referring now to FIGS. 4-4F, application of a separator material isillustrated. Referring particularly to FIGS. 4-4A, the can 10 isprovided with a series of annularly shaped cathode pellets 40. Referringto FIGS. 4B and 4C, a film-forming solution is then applied as spray 55into the interior of the pellets by positioning the probe 22 in the canand initiating nebulization. The probe 22 is drawn upward (arrow 53) toapply a coating 54 of the material along the entire interior surface ofthe cathode. Referring to FIGS. 4D and 4E, the film forming may beinitiated and/or accelerated by application of a second material in aspray 57 from probe 22 in subsequent steps. Referring to FIG. 4F, theanode slurry is provided into the can. The can may then proceed to othersteps such as assembly and crimping of the top assembly.

The film-forming material may be, for example, as described incommonly-assigned Treger et al., “Alkaline Cell with ImprovedSeparator”, U.S. Ser. No. 09/280,367, filed Mar. 29, 1999, now abandonthe entire contents of which is incorporated herein by reference.Preferred materials include polyvinyl alcohol (PVA) solutions which forma hydrogel film by viscosity increase that occurs when the solventevaporates and/or can be thickened by application of a second componentthat is an acid solution, such as KOH electrolyte, which swells the PVAcausing gellation.

In a further embodiment, the electrolyte and film-forming material aresprayed simultaneously. One technique for spraying simultaneously is topremix the PVA and electrolyte at an initial concentration that isstable, i.e. does not induce excessive viscosity increase prior toapplication. A concentration of about 10% to about 15%, preferably about7.5% by weight on a dry basis (W/W) PVA in 9N KOH, having a storage lifeof about 8 h can be used. For most efficient nebulizing, a viscosity ofabout 70 cps or less is preferred. After application, evaporation of thesolvent results in film-forming. A preferred film thickness is about 2mil thick. Alternatively, the PVA and electrolyte may be mixedimmediately prior to nebulization in a Tee positioned just before thenebulizer feed line. In another embodiment, a dual probe nebulizer maybe used, with one nebulizer being plumbed to deliver and spray PVA andthe other plumbed to deliver and spray electrolyte. In anotherembodiment a two lumen probe is used, with one lumen supplied withfilm-forming material and the other with electrolyte. In anotherembodiment, film-forming material and electrolyte are alternativelydelivered to the nebulizer through a flow-switching mechanism.

In other embodiments, the film is formed using cross-linking polymers,including a first component in a polymerization reaction and a secondcomponent that induces cross-linking. Alternatively, cross-linking maybe induced by application of UV or other radiation or heat.Cross-linking of PVA may be carried out as discussed in U.S. Pat. No.4,154,912, the entire contents of which is incorporated herein byreference. Polystyrene films may be formed as described in U.S. Pat. No.4,315,062, the entire contents of which is incorporated by reference. Inapplications where the film forming is facilitated by heat, vibratoryspray application may be used to enhance the film formation. Forexample, application at high power can generate higher temperatures atthe tip which is transferred to the material being applied.

Application to Non-cylindrical Surfaces

Referring to FIGS. 5-5B, the application of a material, in this example,a film-forming material, to a non-cylindrical battery surface, here acathode, is illustrated. The cathode may define lobe-shaped cavities asdescribed in commonly-assigned U.S. Ser. No. 09/358,578, filed Jul. 21,1999 by Bhopendra K. Patel et al. and entitled “Battery”, now U.S. Pat.No. 6,342,317, the entire contents of which is hereby incorporated byreference. The cathode 60, in a can 10, has an undulating lobe shapeincluding regions 62 that are closer to the battery axis 61 and regions64 more distantly spaced from the axis.

Referring to FIGS. 5 and 5A, application of a film-forming separator asa spray 63 using a nebulizer probe (not shown) positioned near the axis61 of the battery can result in deposition in the near regions 62 ofmore material 66 than in the more distantly spaced regions 64 , whichreceive less material 68.

Referring to FIG. 5B, after nebulization is complete, surface tensionand the small surface area and small radius of curvature of the nearregions 62 cause the thickness of the material in the near regions 62 tobe reduced. As a result, a film is formed in which the film in the nearregions is not substantially thinner than in the region 64. Filmuniformity and integrity is enhanced. The can may also be rotated aboutits axis during or after spray application to enhance uniformity byspreading the film by centrifugal force. In further embodiments theprobe may be translated off axis into the lobe-shaped cavities duringnebulization.

EXAMPLE

The following illustrates ultrasonic nebulizing of PVA separatorsolutions. The nebulizer was a Sono Tek BD type nozzle with a conicaltip and operating at 60 Khz (available from Sono Tek, Milton, N.Y.). Thesolutions were sprayed inside glass tubes of about 7 mm and about 4 mm.The solution feed line was jacketed to maintain a temperature of about45 to about 50° C. The probe was heated to about 40° C. by directingflow from a heat gun onto the base. The heat gun flow was terminatedduring spraying.

Two grades of PVA, in solutions having different viscosities, weretested. One solution had a viscosity of about 35 cps (Gohesnol GL-03,13% by weight solids, available from Nippon Gohefei, Osaka, Japan,diluted to 13% by weight solids). The other had a viscosity of about 48cps (Elvanol 51-05, available from Dupont, Wilmington, Del., diluted toabout 10% by weight solids). The solutions are prepared as follows.Using a Silverson L4R dispensing rotor/stator mixer, the material wasdissolved in deionized water at room temperature for 15 minutes. Thesolution was heated to 80-90C. for 45 minutes and let stand overnight toremove air bubble trapped during mixing. An aliquot (2-3 cc) is used todetermine percent of solids by heating at 125° for 10 minutes in a classA recirculating oven. Viscosity can be checked with a Brookfield LVViscometer (#3 spindle at 60 RPM). For the Elvanol solution, 10 g wasdissolved in 90 g of water. For the Gohesnol solution, about 13 g wasdissolved in 87 g of water

The solutions were sprayed at different flow rates and power. The probedispense time was about 1.5 sec. The probe was moved vertically at about0.9-1.1 inch/sec. The results are given in Tables I and II.

TABLE I Gohesnol GL-03 trial (13% b.w. solids, viscosity - 35 cps) Flowrate Run # (cc/sec) Power (W) Comments B1 0.225  8 plume not entirelysymmetrical; piezo crystals misaligned? B2 0.300  8 plume improvesgradually B3 0.375  8 plume improves gradually B4 0.375 12 good plume,good coverage B5 0.500 12 good plume, good coverage B6 0.750 11 goodplume, good coverage

TABLE II Elvanol 51-05 (10% b.w., viscosity 48 cps) Flow rate Run #(cc/sec) Power (W) Comments A1 0.500 6 coverage uneven, but continuousA2 0.375 6 slightly better coverage A3 0.450 7 good coverage

As the results indicate, even coverage was obtained for both PVA grades.To prevent sagging, the films should be immediately wet with electrolyteand drying should be avoided.

Still further embodiments are in the following claims. For example,spray application can be used in the manufacture of zinc-air batteriesto, for example, apply electrolyte or provide a separator.

What is claimed is:
 1. A method for applying a separator to a surface inthe manufacture of a battery, comprising applying a film-forming systemto a surface in a battery container, said system being capable offorming a film and including a first component and a second componentunblended with the first component, wherein said unblended first andsecond components are applied as a spray.
 2. The method of claim 1wherein an average droplet size of the spray is about 5 micron to about30 micron.
 3. The method of claim 1 wherein the spray velocity is about3 to about 5 inch/sec.
 4. The method of claim 1 comprising providing acathode in a can prior to applying said film-forming system, wherein thefilm-forming system is applied to the cathode.
 5. The method of claim 4wherein the film-forming system includes PVA.
 6. The method of claim 5wherein film-forming system includes electrolyte.
 7. The method of claim6 wherein the system is a premixed solution of about 10% to about 15%PVA in KOH electrolyte.
 8. The method of any one of claims 1 to 7wherein said spray is formed by a vibratory nebulizer.
 9. The method ofclaim 1, wherein the first and second components are appliedsimultaneously.
 10. The method of claim 1, wherein the first and secondcomponents are applied sequentially.
 11. The method of claim 1, whereinthe second component comprises an electrolyte.
 12. The method of claim1, wherein the second component comprises a material that facilitatesfilm forming.
 13. The method of claim 1, wherein the surface is definedby a cathode.
 14. The method of claim 1, wherein the surface defines anelongated cavity in a container.
 15. The method of claim 1, wherein thesurface is cylindrical.
 16. The method of claim 1, wherein the surfaceis non-cylindrical.
 17. The method of claim 16, wherein the surfacecomprises an undulating lobe.
 18. The method of claim 1, comprisingmoving an end of a vibratory nebulizer along a length of a batterycontainer.
 19. The method of claim 1, wherein the battery is an alkalinebattery.
 20. The method of claim 1, wherein the battery is a zinc-airbattery.